They only go for tubed starfish (and very rarely urchins but I have yet to see it happen in person. I kept urchins with mine).
Brittles can very easily get away from them too, tubed starfish get flipped and pinned down. They *might* show a feeding response via smell but realistically they couldn't disable them for their very long slow feeding periods.
Ah, yeah, being able to keep it from getting away would be a problem. Though I'd kinda like to see one try to handle a brittle starfish. It'd probably be very confused.